Stare at the red dot in the center of the figure for a minute or two. Before long, the green ring will disappear--it simply seems to fade into the white background. There are no tricks: This is a simple, static image file. The effect has been known for more than two centuries and is named for its discoverer, Ignaz Paul Vital Troxler (1780-1866), a Swiss physician and philosopher. "Troxler fading" is actually related to what you experience when you get "dizzy": You become so habituated to a phenomenon (spinning in a circle or seeing a green ring in your peripheral vision) that you stop noticing it's there.
Or, rather, you don't realize that your perceptual system has begun actively ignoring it. It's only when your circumstances change that you see what the phenomenon has done to your perceptual system. When you stop spinning, the world seems to continue, in reverse. When you look away from the green ring, you see a red ring in the same part of your visual field. From the excellent blog Cognitive Daily.
Something similar to this happens in Media, if we don't hear about it is assumed to have gone away. In many areas of risk, there are risks, I refer to as Oxygen risks, ie things that are so common and pervasive in the environment that we only notice their absence. Liquidity and the efficacy of a Triple AAA rating used to be like that. Flawed or un-considered assumptions due to unchanging environmental factors.
If that green circle doesn't mess with you check out the Change Blindness video. again Courtesy of Cognitive Daily.